The present invention concerns an indirect extrusion process for producing an extrusion product from a hot metal billet, and to an extrusion press and related apparatus for carrying out the indirect extrusion process. The invention further relates to an indirect extrusion process employing a multiple container press turret whereby the containers on the press turret are sequentially rotated through the extrusion axis of the press where the extrusion actually takes place and through various working stations off of the extrusion axis where other functions are performed, such as removing the discard from the press container, cleaning the press container and loading a new billet into the press container.
Extrusion presses employing multiple container turrets of the above type are known. The purpose of such a press is to maximize the efficiency of the press by minimizing the number of operations on the extrusion axis which are not involved in the actual extrusion of the billet. Thus, by performing operations such as discard removal, container cleaning, and billet loading at stations off of the extrusion axis, the press cycle time can be considerably reduced.
Multiple container press turrets are generally employed in connection with a direct extrusion process. In direct extrusion, a die is held tightly against one end of the container and a billet disposed in the cavity of the container is pressed through the die by a ram entering the container cavity from the side opposite the die. The direct extrusion process subjects the container to great axial forces in that the die must be pressed tightly against the one end of the container with sufficient force to withstand the separating forces that occur between the die and container as the billet is pushed through the die. Additionally, the container is subjected to an axial frictional force on its inner surface by the billet as it is being pressed through the container by the ram.
In order to secure the container against axial movement relative to the press turret in the presence of such large axial forces, it has been necessary to secure the container to the turret with a correspondingly substantial retaining mechanism. If it becomes necessary to change a container, for example so that a different diameter billet can be extruded, it can be a painstaking and time consuming process to release such a container from the turret and to secure a different container in its place. Since the entire press is inoperative during the time it takes to change a container, the overall efficiency of the press is greatly reduced.
Indirect extrusion presses are known whereby a container with a billet disposed therein is forced over a stationary die mounted at the end of a hollow stem. The indirect extrusion process eliminates one source of axial force on the container in that the billet does not move with respect to the container so that the axial frictional forces which are incurred in the direct extrusion process are avoided. However, in an indirect extrusion press it is still necessary to seal the back end of the container cavity, and this is generally done by pressing a sealing plate tightly against the back end of the container by a force which is sufficient to overcome the separating forces that occur between the container and the sealing plate. Thus, in the indirect extrusion process the container is also typically subjected to substantial axial forces. In the case of a multiple container turret, it is a complex task fraught with many pitfalls to implement an indirect extrusion process utilizing a conventional sealing plate at the back end of the container. If the indirect extrusion process were to be implemented with a multiple container turret in the conventional manner, the entire turret would have to be axially moveable in order to pass the container over the die, and a substantial axial force on the container would be required to ensure an effective seal by the sealing plate at the back end of the container as previously discussed. This results in a complex solution for fixing axial movement of the container relative to the turret which in turn raises difficulties in terms of overall press efficiency in connection with the changing of a container when this becomes necessary. Multiple container turrets are therefore generally employed in connection with a direct extrusion process rather than indirect extrusion, since the container and turret generally remain axially stationary in the direct extrusion process.